The Field of Digital Radiography Loren Sachs Instructor

What is Digital Radiography? Historically, digital radiography referred to specialized modalities that produced digital images. Examples would include: CT MRI Nuclear Medicine Ultrasound

Digital Radiography Today Since the early 1990s, Digital Radiography has grown to include Computed Radiography(CR) and ‘true’ Digital Radiography(DR) or Direct Radiography. Our lecture today will focus on CR and DR.

Digital Terms Pixel Voxel Picture element. This is the basic component of the digital image, it is what we see. 2 dimensional Voxel Volume element. This is a 3 dimensional element that includes depth. The pixel is essentially the end of the voxel.

Matrix The actual image we see is made up of a series of pixels in rows and columns called a matrix. Generally, the larger the matrix the better the spatial resolution of the image. Bit The amount of gray scale in the image. The bit is the exponent to two, ie, a 2 bit image is two to the second or four. So the image would have 4 shades of gray possible. Today, most images are 10 or 12 bit.

FoV Field of view. This is how much anatomy is displayed. A 12 cm FoV will display 12 cm of anatomy on the screen. The smaller the FoV the more magnified the anatomy is.

Window width Window level The gray scale of the digital image. The larger the width the more grays demonstrated the lower the contrast of the image. Window level The density or brightness of the image. The higher the number the brighter the image.

Computed Radiography The technical aspects of CR are similar to what you see in the traditional analog radiology department, i.e., the technologist exposes a cassette that is then processed. CR differs from analog in that the CR cassette contains a phosphor plate instead of a sheet of film.

CR Overview

The Technology of CR After the cassette is exposed by the x-ray beam, the cassette is loaded into a reader. The reader removes the phosphor plate and exposes it to a laser, stimulating the phosphors. The light emitted from the plate is collected, quantified, and digitized.

CR Processing

Advantages of CR The major advantage of CR is that existing radiology rooms can use the technology. Consequently, the Radiology department can be digital at a relatively low cost, between $100,000-150,000 per reader. Also, due to the similarities with traditional radiography the learning curve is much shorter with CR.

Digital Radiography DR uses no cassette. The image capture device is embedded within the table-top. The advantage here is that the steps involved in processing a ‘cassette’ are eliminated resulting in a huge increase in productivity. Studies have estimated a 100% increase in room throughput.

DR Overview

Technology of Digital Radiography There are two types currently being used Direct Indirect

Direct Digital Radiography The photoconductor is made up of amorphous selenium.

Indirect Digital Radiography The intensifying screen is made up of cesium-iodide crystals and the photodetector is made up of amorphous silicon.

Which DR Methodology is Best? It depends entirely on who you listen to. Basically, different manufacturers are using proprietary technology and claiming theirs is the best. Ultimately, it will be decided by end-users.

DR Issues The significant disadvantage for DR is cost. Normally, rooms with DR technology have to be constructed from the ground up. Today, the average DR room cost is $400,000-600,000 plus construction costs. Construction costs can be overwhelming, particularly in older buildings that need to be brought up to code.

How does CR and DR Affect You the Technologist? RSV is less for both CR and DR when compared to film/screen combinations. Consequently, techniques are going to be higher. Centering and collimation are REQUIRED. You gain a tremendous amount of exposure latitude. Post-processing manipulation allows you to adjust film quality.

How does CR and DR Affect You the Technologist? 2 By selecting processing algorithms you can obtain different anatomical information with one exposure. A PA chest film and be reprocessed as a PA rib film. These methodologies are not a panacea for being a ‘bad’ technologist.

How does CR and DR Affect the Patient and Medical Care? Patient dose goes up with these systems for an individual exam; however, there are fewer repeats. Films are available hospital-wide almost immediately and can be view in multiple locations simultaneously. No films get lost. Everyone associated with a patient’s films becomes more efficient.

Other Considerations In order to gain maximum efficiency with CR and DR a RIS/PACs systems needs to be deployed. RIS, Radiology Information Systems, are used to manage non-image patient data, i.e. exam number, dictation status, and billing. PACs, Picture Archiving Computer, allows for the distribution of images over a pre-described area.

Conclusion Digital radiography will change the way technologists practice radiography. However, it will not eliminate the need for a quality education and an understanding of radiology principles. In fact, digital radiography will require additional learning in order to maximize its usefulness.